Olet or Instrument Adaptor Failure in Jacketed Piping System: Causes and Prevention Through Pipe Stress Analysis

Abstract This paper presents the cause analysis of an Olet or Instrument adaptor Failure in Jacketed Piping System Operating in a Process Plant, which is welded to the core and the jacketed pipe. Failure in Olet or Instrument adaptor is primarily attributed to Thermal difference (LCF) and VIV (HCF), which is represented by comprehensive computer analysis applications like ANSYS (Finite element analysis) & CAESAR II to calculate Thermal effect, Vibration modes, Frequencies, Stress, Fatigue life Prediction & Design optimization. In Jacketed Piping, Small bore or instrument piping connections such as Pivot tubes, Sample Analyzer probe, thermowell, Chemical injection etc., are often overlooked during the design phase. This oversight can lead to premature failure of the instrumentation piping connected to both the core and jacket due to the significant effects of differential thermal expansion and VIV. For VIV, natural frequency of the thermowell submerged inside the fluid of the core pipe is not screened for the Vortex induced effect as suggested by ASME PTC19.3 TW 2016 [2], which leads to a catastrophic failure due to the resonance, when the frequency generated by the fluid flow is in-lined with the thermowell’s wake frequency. The case study in this paper will explore both simple and complex preventative measures tailored to various disciplinary requirements, including Relocation of Olet, Discontinuous Jacket Arrangement, Robust Instrumental piping Design, Isolated Olet Fabrication, Extruded Cap Fabrication, and earlier periodic replacement for Olet or Instrument Adaptor.